LEMs are supposed to simulate light sources, not physical materials. This is not really how LEMs are supposed to be used.

The thing about this scene is that only a single plane is distorted, which is odd. We also don't know how you have configured the material, and what the material assignments are to the front and back face.

The way the scene ought to be configured, is to model the object as you would expect to find it in reality. Those sides would either be made of a single sheet of perspex which has different colours, or are separate sheets of coloured material. The light colour would be an opal polycarbonate or translucent filmed glass with a light source behind.

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